Pebble heater



Jan. 29, 1957 R. A. FINDLAY PEBBLE HEATER Filed Jan. 2, 1952 INVENTOR. R. A.F|NDL AY BY 2 ATLIORNEYS United States Patent PEBBLE HEATER Robert A. Findlay, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Application January 2, 1952, Serial No. 264,590

19 Claims. (Cl. 263-19) This invention relates to pebble heaters. In one of its more specific aspects, it relates to improved pebble heater apparatus. In another of its more specific aspects, it relates to a Single shell pebble heater apparatus. In another of its more specific aspects, it relates to pebble heater apparatus having only a single upright chamber containing a contiguous gravitating mass therein. In another of its more specific aspects, it relates to the conversion of hydrocarbons in pebble heater apparatus.

Apparatus of the so-called pebble-heater type. has been utilized in recent years for the purpose of heating fluids to elevated temperatures. Such apparatus is especially suited for use in temperature ranges above those at which the best available high temperature structural alloys fail. Thus, such equipment may be used for superheating steam or other gases and for the pyrolysis of hydrocarbons to produce variable products such as ethylene and acetylene, as well as for other reactions and purposes. Conventional pebble heater-type apparatus in- .cludes two refractory-lined contacting chambers disposed tone above the other and connected by a refractory-lined zpassageway or pebble throat of relatively narrow cross :section.

Refractory solids of flowable size and form, called -pebbles, are passed continuously and contiguously :through the system, flowing by gravity through theupper- .rmost chamber, the throat, and the lowermost chamber, .and are then conveyed to the top of the uppermost cham- ..ber to complete the cycle.

Solid heat exchange material which may be used up to ctemperatures of about 4000 F. in the pebble heater apparatus is similar to that described in U. S. Patent 2,505,256 issued to Donald J. Quigg.

The pebbles are heated in one of the chambers (preferably the upper one) by direct contact therein with hot ;gases, usually combustion products, to temperatures gentotally in the range of 1400 F. to 3200 F. The hot pebbles are thereafter contacted with the fluid to be superheated or reacted, as the case may be, in the other chamber. Generally, pebble inlet temperatures in the second chamber are about 100 F. to 200 F. below the highest temperature of the pebbles within the first chamber. 1n processes for the production of ethylene, light hydrocarbons, such as ethane, propane, or butane, the pebble temperature in the reaction chamber is usually in the range of 1200 F. to 1800 F. For the production of acetylene by pyrolysis of hydrocarbons, temperatures in the range of 1600 F. to 3000 F. are desirable.

In the past, considerable trouble has been encountered in the operation of pebble heater apparatus for the reason that pebbles which are heated in the pebble heating chamber are not all heated to auniform temperature. For this reason the pebbles which are introduced into the upper end portion of the reaction chamber lack the de sired uniformity of temperature which would give the best reaction of feed within that reaction chamber. The result has been that a portion of the feed stock has been overcracked and a portion of the feed stock has been 2,779,658 Patented Jan. 29, 1957 undercracked by reason of the contacting with pebbles heated to temperatures above and below that desired for reaction of the feed. This difficulty in obtaining uniform temperatures of pebbles within the pebble heating chamber is due principally to the fact that the pebble heating chamber is one of large cross section, and the gas flow patterns within such a chamber containing a contiguous gravitating pebble mass are such as to permit a considerably greater contact time between gas and pebbles in one section of the chamber than is obtained in another section of the same chamber.

Another disadvantage of the conventional pebble heater type apparatus is that it is quite expensive to construct, partly because of the fact that the two chambers should be supported one above the other so as to obtain gravitating flow of pebbles throughout the entire length of the system. Such a structure requires a considerably greater supporting structure than is necessary for one of lesser length. Another disadvantage in construction of the conventional pebble heater type apparatus is that a long elevator system is necessary, thus, posing many operational problems.

By at least one aspect of this invention, at least one of the following objects of the invention is attained.

An object of this invention is to provide improved pebble heater apparatus. Another object of the'invention is to provide a single chamber pebble heater apparatus. Another object of the invention is to provide an improved method for reacting hydrocarbons in pebble heater apparatus. Another object of the invention is to provide an improved method for heating; pebbles in pebble heater apparatus. Other and further objects and advantages will be apparent to those skilled in the art upon study of the accompanying discussion and the drawings.

Broadly speaking, this invention comprises a single chamber pebble heater apparatus, the single chamber forming a single zone for reaction or treatment of gaseous materials within that chamber. The entire amount of pebble heating is obtained in the pebble recycle system utilized for elevating the pebbles which are removed from the bottom of the reaction chamber to the upper end portion of the chamber. A gas-lift type of recycle system is utilized for returning the pebbles to the upper end portion of the reaction chamber. The lift-gas is heated to a high temperature prior to its contact with the pebbles. In this manner, each of the pebbles returned to the upper end of the reactor is delivered at substantially the same temperature as any other pebble, thereby obviating the difficulty of non-uniform pebble heating. It should also be noted that the elevator system which is utilized in connection with this invention can be about one-half the length of that required in systems wherein two chambers are disposed one above the other.

Better understanding of this invention will be obtained upon reference to the drawing which is a schematic flow diagram of the pebble heater system and feed and efiluent lines connected with such a. system.

Referring particularly to the device shown in the drawing, pebble heater apparatus 11 comprises an upright elongated shell 12, closed at its upper and lower ends by closure members 13 and 14, respectively. Pebble inlet conduit 15 extends into the upper end portion of shell 12, preferably being centrally disposed in closure member 13. It is Within the scope of this invention, however, to utilize a plurality of pebble inlet conduits uniformly disposed over the top of the pebble heater apparatus. Gaseous effiuent conduit 16 is provided in the upper end of shell 12, preferably in closure member 13. Pebble outlet conduit 17 extends downwardly from the bottom of shell 12, preferably from the lower end of closure member 14. Pebble outlet conduit 17 is connected at its '1. 0.? lower end to the lower end of elevator 18, which elevator extends upwardly into the central portion of gas-pebble separator chamber 19. Pebble inlet conduit is connected at its upper end to the lower end portion of separator 19.

Gaseous inlet conduit 21, having flow control valve 22 provided intermediate its ends, is connected to the lower end portion of pebble inlet conduit 15. Gaseous material inlet header Z3 is provided so as to at least partially encircle pebble inlet conduit 15 intermediate its ends and communicates with the interior of the pebbleinlet conduit. Gaseous material outlet conduit 24 is connected to the upper end portion of pebble inlet conduit Eat a point downstream of separator chamber 19. Separator chamber 25 is connected intermediate its ends to the upper end portion of separator chamber 19 by means of conduit 26. Indirect heat exchanger 27 is connected to the upper end portion of separator '25 by means of conduit 23, that conduit being provided with how control valve 29 intermediate its ends. Conduit 31. extends from indirect heat exchanger 27 and is connected 'to vent conduit 32 having flow control Valve 33 provided intermediate its ends. Outlet conduit 31 is also connected to conduit 34 which is inturn connected to 'a pressurizer, such as blower 35. Conduit 34 is pr'ovided with flow control valve 36 intermediate its ends and an inlet conduit 37, provided with flow control valve 38, is connected to conduit 34 intermediate flow control valve 36 and blower 35. Conduit 24 is directly connected'to conduit 23 by means of by-p'assconduit 39, the latter conduit being provided with a flow control valve 41 intermediate its ends. A second by-pass conduit 42, being provided with a flow control valve 43, connects conduit 24 directly with conduit 34 at a point upstream of flow cc ntrol valve 36. Feed conduit 44 extends through indirect heat exchanger 27 and through an auxiliary indirect heat exchanger 45 and is connected'to the lower endof shell 12 and communicates with the chamber within that shell, preferably through bottom closure member 14.

Combustion chamber or furnace 46 is formed'as an indirect heat exchanger, the furnace being divided into two sections by means of a refractory baffle 47. Air and fuel inlet conduits 48 and 43, respectively, are connected to furnace 46 on one side of baffle member 47. Although the-furnace and heat exchanger are shown in a preferred form" as a single unit, they can be formed separately and combustion gas used to ,heat the exchanger. Combustion gas outlet conduit 51 extends from'the portion of the combustion chamber connected to the air'and fuel inlet conduits. Conduit 51 is divided into two portions, one portion 5 2 being connected to indirect heat exchanger 45 and having a flow control valve 53 provided inter mediate its ends. A gaseous material-outlet conduit 54 extends from the downstream end of indirect heat exchanger 45.

The second portioni of combustion gas conduits is designated as conduit 55 having flow control valve 56 provided intermediate its ends. Conduit 55 is in turn divided into two portions, one portion being designated as conduit 57, which conduit is connectedat its downstream end to inlet header 2 3. Conduit 57 is provided'intermediate its ends with a flow control valve 58. The second portion of conduit 55 is designated as I conduit 59 and is connected to thelower end of gas lift 18. Flowcontrol valve 61 is provided intermediate the ends of conduit 59. Conduit 62 extends from blower'35 to the upstream endof the section of furnace 46 which is not connected with the fuel and air inlet conduits.

Flow control valve 63 is provided intermediate the ends of conduit 62. Conduit 64 extends frornthe downstream end of the section of furnace 46 which is connected to conduit '62 and is connected at its downstream end to conduit'59 downstream of flow control valve 61. A pebble flow controller 65 is provided intermediate the ends "of pebble "outlet 'conduit 17. 'This flow controller may be any one of the conventional controllers, such as a star valve, a gate valve, a rotatable table feeder, or the like.

In the operation of the pebble heater of this invention, pebbles are introduced into the upper end portion of chamber 11 through pebble inlet conduit 15 and form a contiguous gravitating gas pervious mass within that zone. This mass of pebbles continues as a contiguous bed downwardly through the entire length of the chamber and through pebble outlet conduit 17 to pebble flow controller 65. The pebbles are fed by means of pebble feeder 65 into the lower end portion of gas-lift elevator 18. A lift-gas is introduced into the lower end portion of elevator 18 at a temperature of at least about 2000 F. and at a sufiicient volume and velocity to entrain the pebbles and elevate them to the upper end of the elevator. When the pebble-entraining gas stream enters separator 19, the velocity of the pebbles is so reduced as to allow those pebbles to settle from the gas stream within separator 1-9.

In one aspect of the invention, fuel and air are introduced into furnace '46 through conduits 48 and 49. The fuel and air are burned and the resulting hot combustion products are passed by meansof-conduits 51,55-and 59 to the lower end of elevator 18. The e'filuent gas is removed from the upper end portion of chamber 19 through conduit 26. This effluent gas carries with it the pebble fines from the system and 'is passed through separator chamber 25, which is a -cyclone-type separator. The

pebble fines are separated from the eflluent gas and are removed from the bottom portion of that chamber. The effluent gas is removed from the upper end portion of separator chamber 25 and 'is passed 'throughindirect'heat exchanger 27-and is removed from the system'through outlet conduit 31 and vent conduit 32.

:The'feed to the pebble heater system whetheriitgbe a hydrocarbon feed or a gaseous materialto be treated, ispassed by conduit 44 throughindirect heatexchanger 27' in indirect heat exchange with the gaseous effluent from the gas-lift. A second portion of the combustiongases obtained from furnace 46 is passed by means of conduit 52 into" indirect heat exchanger 45 and iszvented-through conduit54. The feed which is preheated inttheindirect 'heat exchange in exchanger 27 ispassed through indirect heat exchanger 45 and is additionally preheated by means of a second portion of combustion gas from furnace 46 in'the indirect heat exchange within exchanger 45. The

preheated feed is then introduced into the lowerportion "of chamber 12.

In elevating the pebbles to theupper end-portion of: the

elevator, it is necessary to maintainLapebbIevelocity at thetop of the lift of at least 5 feet-1 per second. It isithus necessary-to introduce asufficientvolume ofwgasinto the-lower'end of the. gas-lift to move therpebblesrata particular lift-gas utilized. When a shortertliftis utilized,

' a smaller initial pebble velocity may be usedand when 60- a; longer pebble lift is used a larger initial pebble velocity will be required.

Combustion products resulting from the burning 0f. :a hydrocarbon feed and airare satisfactorily utilized as one lift-gas. It is preferred to utilize inlet lift-gas temperatures in the range of-between 2000 and 320 0 F.

It also'is preferred to preheat the gaseous-feed in an indirect heat exchange to a temperatureclose-to its cracking temperature, if the feed is a hydrocarbon feed.

Somewhat higher pebble temperatures canbe obtained in the gas-lift by burning oxygen and hydrogen iinathe furnace and utilizing the resulting steam; product asihe lift-gas. When steam is utilized as the lift-gas, it-lwillbe necessary to utilize a "higher initial-pebble velocityuin the lower 'portion. of the gas-lift'than is used .whemprodnets of hydrocarbon combustion are used as the lift-gas,

in order to obtain the final lift of the pebbles in the top of the gas-lift ata velocity of about 5 feet per second. In another aspect of this invention, a gaseous material such as methane or hydrogen is introduced into conduit 34 through flow control valve 38 and conduit 37. This gaseous feed is pressurized in blower 35 and is passed by means of conduit 62 into the portion of furnace 46 which is not connected with inlet conduits 48 and 49. The gaseous feed is heated to a high temperature, preferably at least 2400 F. by means of the indirect heat exchange with the combustion products and by radiant heat within furnace 46. The preheated gaseous material is then passed into the lower portion of gaslift 18 by means of conduit 64 and conduit 59. The advantage which is obtained by use of these gases as the lift-gas material is that the pebbles can be heated to a somewhat higher temperature than when products of hydrocarbon combustion are used. A feed of hydrogen provides a substantially higher temperature for the pebbles than does the preheated methane. When. methane is used as the lift-gas, a portion of that gas is cracked during the heating and lift steps. After the methane and its products are removed from the upper end of separator chamber 19 and are passed through indirect heat exchanger 27 they may be vented to the atmosphere but are preferably utilized as a preheated feed for furnace 46. When hydrogen is used as the lift-gas, the hydrogen is removed from the upper end portion of separator chamber 19, passed through separator and indirect heat exchanger 27. When utilizing this type of lift-gas, it is ordinarily not necessary to utilize the auxiliary heat exchanger 45 for preheating the feed. However, the auxiliary heat exchanger 45 may be utilized so as to obtain the desired feed temperature. The hydrogen removed from indirect heat exchanger 27 is passed by means of conduits 31 and 34 into blower 35 wherein it is pressurized and once again recycled through the indirect exchange in furnace 46 and into the lower end of gas-lift 18.

As pointed out above, one of the important features of this invention is that each of the pebbles is raised to a temperature which is substantially the same as the temperature of each of the other pebbles. In one additional aspect of this invention, a final heating is obtained by passing a portion of the combustion products from furnace 46 through conduits 55 and 57 into header memlber 23. That hot gas is then passed upwardly through pebble inlet conduit 15 to outlet conduit 24. Pebble inlet conduit 15 is considerably smaller in cross section than .any of the conventional pebble heater chambers and for 1this reason the heating which is obtained within conduit 115 is substantially the same for all pebbles. An increase of 200 F. to 300 F. in pebble temperature can be ob- :tained in this short section of the pebble inlet conduit by direct heat exchange with a relatively small volume of the heating gas. The heating gas is removed from inlet conduit 15 through conduit 24 and may be passed through conduit 39 and indirect heat exchanger 27 or may bypass indirect heat exchanger 27 by means of conduits 42. The gasis then disposed of as disclosed above. When hydrogen is used as the lift-gas, a portion of the hydrogen stream may be diverted through conduit 59 and conduit 57 to header 23 and be used to heat the pebbles within pebble inlet conduit 15.

Many modifications of this invention will be apparent upon study of the disclosure and the drawing. These modifications are believed to be within the spirit and the scope of this invention.

I claim:

1. An improved pyrolysis system which comprises a closed, upright, elongated shell inclosing a single chamber; pebble inlet means in the upper end of said shell; gaseous effluent means in the upper end of said shell; pebble outlet means in the lower end of said shell; gaseous material inlet means in the lower end portion of said 6 shell; pebble feeder means intermediate the ends of said pebbleoiitlet means; an upright gas-pebble conduit connected at its lower end portion to the lower end of said pebble outlet means and extending to a level above the top of said shell; a gas-pebble separator chamber connected to the upper end of said gas-pebble conduit; a pebble conduit connecting said pebble inlet means and the lower end portion of said separator chamber; a source of hot lift gas outsideof said gas-pebble conduit and outside of said shell; lift-gas inlet means connected to the lower end of said gas-pebble conduit and to said source of hot lift gas; and gaseous material effluent means in the upper end portion of said separator chamber.v

2. The improved pyrolysis system ofclaim 1 wherein a heating gas inlet conduit is connected to said pebble conduit intermediate its ends; and a gaseous effluent conduit is connected to said pebble conduit near its upper end.

3. An improved pyrolysis system which comprises a closed, upright, elongated shell inclosing a single chamber; pebble inlet means in the upper end of said shell; gaseous efi'luent means in the upper end of said shell: pebble outlet means in the lower end of said shell; gaseous material inlet means in the lower end portion of said shell; pebble feeder means intermediate the ends of said pebble outlet means; an upright gas-pebble conduit connected at its lower end portion to the'lower end of said pebble outlet means and extending to a level above the top of said shell; a gas-pebble separator chamber enclosing the upper end portion of said gas-pebble conduit; a pebble conduit connecting said pebble inlet means and the lower end portion of said separator chamber; lift-gas inlet means connected to the lower end of said gas-pebble conduit; a second separator chamber; an effluent conduit extending from the upper end portion of said separator chamber to a point intermediate the ends of said second separator chamber; a first indirect heat exchanger; a gaseous effluent conduit extending between the upper end portion of said second. separator chamber and said first indirect heat exchanger; effluent outlet means extending from said first indirect heat exchanger; a feed conduit extending through said first indirect heat exchanger and connected to said gaseous material inlet means in the lower end portion of said shell; a heating gas inlet connected to said pebble conduit intermediate said pebble inlet means and said separator chamber; a gaseous efiluent conduit extending from the upper end portion of said pebble conduit; a furnace outside of said shell and outside of said gas-pebble conduit; combustible material inlet means connected to said furnace; and conduit means connecting said furnace and said heating gas inlet in said pebble conduit.

4. The pyrolysis system of claim 3 wherein said gaseous effluent conduit from said pebble conduit is connected at its downstream end to said first indirect heat exchanger.

5. The pyrolysis system of claim 3 wherein a second indirect heat exchanger is operatively connected to said feed gas conduit intermediate said first indirect heat exchanger and said shell; a gaseous material conduit extends between said furnace and said second indirect heat exchanger; and eflluent conduit means extends from said second indirect heat exchanger.

6. An improved pyrolysis system which comprises a closed, upright, elongated shell inclosing a single chamber; pebble inlet means in the upper end of said shell; gaseous effluent means in the upper end of said shell; pebble outlet means in the lower end of said shell; gaseous material inlet means in the lower end portion of said shell; pebble feeder means intermediate the ends of said pebble outlet means; an upright gas-pebble conduit connected at its lower end portion to the lower end of said pebble outlet means and extending to a level above the top of said shell; a gas-pebble separator chamber enclosing the upper end portion of saidgas-pebble con- ,duit; a pebble conduit extending between the upper end .portion of said pebble inlet means and the lower end portion of said separator chamber; lift-gas inlet means connected to the lower end of said gas-pebble conduit; asecond separator chamber; a conduit extending between the upper end portion of said gas-pebble separator chamberand a point intermediate the ends of said second separator chamber; a first indirect heat exchanger; a conduit extending between the upper end portion of said second separator chamber and said first indirect heat exchanger; a gaseous efiluen t conduit extending from said first indirect heat exchanger; a feed gas conduit extending through said first indirect heat exchanger and connected "at its downstream, end to said gaseous material inlet means; a furnace outside of said shell and outside of said gas-pebble conduit; combustible material inlet means connected to said furnace; gaseous effluent conduit means extending from said furnace; a second indirect heat exchanger operatively connected to 'said furnace; a first liftgas conduit connected to the upstream end of said secondindirect heat exchanger; a second lift-gas conduit extending between the downstream end of said second indirect heat exchanger and said lift-gas inlet means; and a pressurizer intermediate the ends of said first lift-gas conduit.

7. The pyrolysis system of claim 6 wherein a third indirect heat exchanger is operatively connected to said feed conduit intermediate said first indirect heat exchanger and said shell; a conduit extends between said furnace and said third indirect heat exchanger; and a gaseous eflluent conduit extends from said third indirect heat exchanger.

8. The pyrolysis system of claim 6 wherein a heating gas inlet is connected to said pebble conduit intermediate said pebble inlet means and said gas-pebble separator chamber; a gaseous eilluent conduit extends from the upper end portion of said pebble conduit and is connected to said efiiuent conduit from said first indirect heat exchanger; and a heating material conduit extends from said gaseous efiluent conduit means extending from said furnace to said heating ga inlet in said pebble conduit.

9. The pyrolysis system of claim 8 wherein said gaseous material conduit extending from the upper end portion of said pebble conduit is connected to said efiluent conduit from said first heat exchanger through said first heat exchanger.

10. The pyrolysis system of claim 8 wherein a gaseous material conduit extends between said efiluent conduit from said first indirect heat exchanger to said first heating gas inlet conduit upstream of said pressurizer.

11. The pyrolysis system of claim 6 wherein said furnace is a tube furnace and said first heating gas conduit and said second heating gas conduit are connected to the tubes of said furnace at the upstream and downtream ends, respectively. 7

12. An improved method for operating a pebble heater which comprises the steps of introducing hot pebbles into the upper end of a single chamber for heating a gas by heat exchange with said pebbles; gravitating said pebbles downwardly through said chamber as a contiguous gas-pervious mass; gravitating said pebbles from the lower end of said chamber at a controlled rate into the lower end portion of a gas-lift conduit; burning a combustible material outside of said chamber and outside of said gas-lift conduit to form hot gaseous entraining fluid; passing said hot gaseous entraining fluid into the lower end portion of said gas-lift conduit in sufficient volume to entrain said pebbles and elevate said pebbles to the upper end portion of said gas-lift conduit, whereby the temperature of said pebbles is elevated to a desired temperature by direct heat exchange with said hot gases; separating said lift-gas and said pebbles at the upper end of saidgas-lift conduit; g'ravitating said heated pebbles through a communication z'onedirectly into the upper end portion of said single chamber; introducing a gaseous feed into the lower end position of said chamber"; passing said gaseous feedupwardly through said contiguous gaspervious pebble mass within said chamber countercurrent to the gravitatingpebble flow, whereby said gaseous material is elevated to a desired temperature within said chamher; and removing gaseous eflluent from the upper end portionof said chamber. k

, 1-3. The method of claim 12 wherein 'said entraining fluid is introduced "rats the lower end portion of said gas-lift conduit at a temperature within the range of between 2000 and 3200 F.

14. The method of claim 13 wherein said ent'raining fluid is introduced into the lower end of said gas-lift at a temperature of at least 2400 F.

15. T he method of claim 13 wherein said combustible materials are hydrogen "and oxygen and steam is the resulting combustion product introduced into the lower end; portion of said gas-lift conduit.

16. The method offclaim 15 wherein a portion of -said entraining fluid is introduced into the gravitating mass of pebbles intermediate the ends of said communication zone and is passed upwardly through said gravitati ng mass of pebbles to a point near the upper end of said gas-lift conduit to further heat said pebbles; and the gaseous effiuent from the upper end portion of said communication zone is removed adjacent the upper end of said gas-lift conduit.

17. The method of claim 13 wherein said feed gas is preheated by indirect heat exchange with said gaseous efiluent from said gas-lift conduit.

18. The method of claim 12 wherein said lift-gas is heated to a temperature within the range of between 2000 F. and 3200 F. in indirect heat exchange with the combustion of combustible materials in a combustion chamber.

19. An improved pyrolysis system which comprises a closed, upright, elongated shell; pebble inlet means in the upper end of said shell; gaseous elfluent means in the upper 'end of said shell; pebble outlet means in the lower end of said shell; gaseous material inlet means in the lower end portion of said shell; pebble feeder means intermedia'te the ends of said pebble outlet means; an upright gas-pebble conduit connected at its lower end portion to the lower end of said pebble outlet means and extending to a level above the top of said shell; a gas-pebble separator chamber connected to the upper end of said gas pebble conduit; a pebble conduit connecting said pebble'inlet means and the lower end portion of said separator chamber; a source of hot lift gas outside of said shell and outside of said gas-pebble conduit; conduit means connecting said source with the lower end of said gas-pebble conduit below its juncture with said pebble outlet means, said gas-pebble conduit comprising the sole means of heating pebbles in said system; and an outlet for gaseous effluent from the upper end portion of said separator chamber.

References (Zited in the file of this patent UNITED STATES PATENTS 

1. AN IMPROVED PYROLYSIS SYSTEM WHICH COMPRISES A CLOSED, UPRIGHT, ELONGATED SHELL INCLOSING A SINGLE CHAMBER; PEBBLE INLET MEANS IN THE UPPER END OF SAID SHELL; GASEOUS EFFLUENT MEANS IN THE UPPER END OF SAID SHELL; PEBBLE OUTLET MEANS IN THE LOWER END OF SAID SHELL; GASEOUS MATERIAL INLET MEANS IN THE LOWER END PORTION OF SAID SHELL; PEBBLE FEEDER MEANS INTERMEDIATE THE ENDS OF SAID PEBBLE OUTLET MEANS; AN UPRIGHT GAS-PEBBLE CONDUIT CONNECTED AT ITS LOWER END PORTION TO THE LOWER END OF SAID PEBBLE OUTLET MEANS AND EXTENDING TO A LEVEL ABOVE THE TOP OF SAID SHELL; A GAS-PEBBLE SEPARATOR CHAMBER CONNECTED TO THE UPPER END OF SAID GAS-PEBBLE CONDUIT; A PEBBLE CONDUIT CONNECTING SAID PEBBLE INLET MEANS AND THE LOWER END PORTION OF SAID SEPARATOR CHAMBER; A SOURCE OF HOT LIFT GAS OUTSIDE OF SIAD GAS-PEBBLE CONDUIT AND OUTSIDE OF SAID SHELL; LIFT-GAS INLET MEANS CONNECTED TO THE LOWER END OF SAID GAS-PEBBLE CONDUIT AND TO SAID SOURCE OF HOT LIFT GAS; AND GASEOUS MATERIAL EFFLUENT MEANS IN THE UPPER END PORTION OF SAID SEPARATOR CHAMBER. 